The present invention relates to a testing apparatus for simulating the behavior of contacts in machine components moving under normal force action with at least two test objects including at least one first test objects which performs a rolling movement with or without a superimposed sliding movement on a second test object. For example, such apparatuses are required for simulating the engagement conditions of meshing gears.
The investigation of the permissible loading or stressing of meshing gears has long caused problems. These problems more particularly occur if, as is normally the case, the gears are lubricated. During tooth engagement, there is a change to the tangential velocities of the meshing tooth profile surfaces, the radii of curvature and, on passing from double to single engagement, the normal force. Moreover, due to their contraform design, tooth profiles are elastically deformed during loading and the lubricant is heated due to the frictional heat produced during engagement, so that the problem can only be theoretically solved in an approximate manner and with considerable programming and calculating expenditure on large computers.
Thus, considerable importance is still attached to the experimental investigation of tooth engagement. Due to the complicated engagement geometry and kinematics of the tooth system, attempts have been made to simulate tooth engagement in a so-called two disk or wheel test stand. However, such test stands suffer from the disadvantage that the change to the velocity for the engagement cannot be simulated. It is only possible to simulate individual operating points on the engagement path under stationary conditions and simulation thereof is not possible because of the non-stationary engagement conditions resulting from the change in the tangential velocity. The frequently used four disk or wheel test stands can also only be used for stationary operating conditions. Their main advantage compared with two disk test stands is that as a result of the symmetrical load application to the central disk, the latter can be mounted in an over high manner, which is more favorable from the measurement standpoint.
The experimental investigation of lubricated tooth systems causes particular difficulties. .The most frequently encountered wear phenomena on lubricated tooth systems are scoring or fretting on the one hand and pitting on the other. Scoring mainly occurs on the tooth tips or crests, whereas pitting frequently occurs in the vicinity of the pitch point. Thus, scoring occurs in the area where the sliding velocity, i.e. the difference between the tangential velocities of the two profiles is high, whereas pitting occurs in the area where the sliding velocity is low or zero.
Theoretical research, confirmed by tests on disk test stands, reveals that the wear is essentially determined by the thickness of the lubricating film which builds up between the contact bodies. The known DOWSON formula for the approximate calculation of the lubricating film thickness states that the minimum lubricating film thickness in contact h.sub.min is proportional to the instantaneous tangential velocity of the tooth profiles u.sub.0.sup.0.7. u.sub.0 being the arithmetic mean of the tangential velocities of the two profiles. Thus, during simulation, particular importance is attached to adapting the velocity conditions of the simulation apparatus to those of the tooth system.
Experimental research has also revealed that the results provided by disk test stands with respect to the formation of scoring and pitting can only be inadequately transferred to tooth systems, which can inter alia be attributed to differences in the velocity patterns. The variations are so great that tooth systems are used for investigating wear in the presently standardized wear tests, such as e.g. the FZG test according to DIN 51354. However, these tooth systems must be manufactured with high accuracy and ground and are consequently very expensive. Since, in addition, series results are necessary in order to obtain statistically informative test results, enormous cost are involved in such wear research.
German Specification No. 31 40 661 discloses an apparatus for simulating the stresses of gears rolling on one another with rotationally symmetrical disks, in which each disk is mounted in non-rotary manner on a swinging or rocking lever, the rotation axis of one lever being located on one side and the rotation axis of the other lever on the other side of the two disks, which are pressed together by bracing. A combined rolling/sliding movement is achieved by the movement of the swinging lever. This known apparatus has proved satisfactory, particularly when simulating the engagement conditions in slowly rotating, large gears. However, this apparatus is less suitable for simulating the engagement conditions of smaller, rapidly rotating tooth systems, because here the inert masses of the overall system become disadvantageously apparent.